Story: The Tenth Planet

The Doctor, Ben and Polly arrive at a south pole space tracking station in 1986 where they discover the staff are having problems. A new planet has been detected heading towards Earth which is a mirror image of our own planet. The base is stormed by tall, part-robotic, part-human creatures – Cybermen. The Doctor reveals that the planet heading for Earth is called Mondas; the Earth's sister planet thousands of years ago until a disaster caused it to break away and drift to the edge of galaxy. The Cybermen start draining Earth of its power to restore their own planet. The staff, along with Ben, overcome the Cybermen using the radiation rods from the base's reactor, but the Doctor is unable to help as he has fallen ill. The Cybermen's plan starts to falter and their planet is eventually destroyed after it absorbs too much power. Polly and Ben help the weakened Doctor back to the Tardis where he falls to the floor and his features begin shimmer and change.

Production notesThe production team were faced with a unique challenge: how do you continue a show if the man playing the lead character wants to leave? William Hartnell had decided it was time to move on, his declining health being a contributing factor. As so little was known about the Doctor's past – what he was or where he was from – they decided that one of the traits of his race would be that its members could cheat death by replacing every single cell in their bodies in an instant, but at the same time change their appearance and personality. This masterstroke effectively set up Doctor Who as a programme that could run as long as it had an audience, giving producers the ability to plausibly recast the main character as the same person, just different. It was a brave but risky move, as the audience could have been alienated by a 'stranger', and Doctor Who's success throughtout the late 60s can in part be attributed to the casting of Patrick Troughton, a well-regarded character actor.